Pediatricians: Keep Thimerosal in Vaccines

Action Points

The American Academy of Pediatrics has endorsed the World Health Organization's stance that thimerosal, a mercury-based preservative, should be left in vaccines and should not be subject to a ban contained in a draft treaty from the United Nations Environment Program (UNEP).

Note that thimerosal allows the use of multiuse vials, and that a thimerosal ban could threaten access to certain vaccines, such as tetanus toxoid, diphtheria-tetanus-whole cell pertussis, and hepatitis B vaccines, around the world.

The American Academy of Pediatrics has endorsed the World Health Organization's stance that thimerosal -- a mercury-based preservative -- should be left in vaccines and should not be subject to a ban contained in a draft treaty from the United Nations Environment Program (UNEP).

In a brief statement published online in Pediatrics, the academy supported the recommendations drafted by the WHO's Strategic Advisory Group of Experts (SAGE) on immunization at an April meeting. An AAP spokesperson said that the endorsement was adopted unanimously by the academy's infectious diseases committee.

The Pediatrics Infectious Diseases Society and the International Pediatric Association have also thrown their support behind the guidance.

In 2009, UNEP requested that an Intergovernmental Negotiating Committee develop a binding treaty to reduce the hazards of environmental mercury. Included in the draft treaty, which will be debated and possibly finalized next month, is a provision banning the use of thimerosal in vaccines.

The WHO has called for the removal of that provision, with SAGE concluding that although it supports efforts to reduce environmental mercury, "it is essential that access to thimerosal-containing vaccines is not restricted under this global initiative."

An Evolving Position on Thimerosal

Thimerosal has been used to prevent the growth of bacteria and fungi in multidose vials of vaccines since the 1930s. In recent decades, concerns have been raised about the potential neurotoxic effects of the preservative and a possible association with autism because it contains mercury in the form of organic ethyl mercury.

The FDA tackled the issue in the late 1990s, and its review showed that the cumulative amount of mercury from vaccines included in the routine immunization schedule for infants could exceed the safety threshold set by the U.S. Environmental Protection Agency based on studies of methyl mercury. The amount did not, however, rise above the thresholds established by federal guidelines from the Agency for Toxic Substance Disease Registry and the FDA.

Based on those findings, and in addition to growing public pressure driven by congressional hearings and increasing media attention on potential adverse neurodevelopmental effects of thimerosal, the AAP and the U.S. Public Health Service (USPHS) in 1999 called for the removal of mercury from all vaccines.

"Once the FDA calculations revealed that even one federal guideline was exceeded, the AAP and USPHS were obligated to full public disclosure," explained Louis Cooper, MD, of Columbia University in New York City, and Samuel Katz, MD, of Duke University in Durham, N.C., in a commentary accompanying the academy's current endorsement.

"With that disclosure, it was important to demonstrate a response that could prevent exceeding the guideline levels and also to continue to protect infants by still ensuring full immunization," wrote Cooper, a member of the AAP board of directors in 1999, and Katz, a former chair of the academy's infectious diseases committee. "The joint statement met those obligations while demonstrating an abundance of caution: putting safety first."

By 2001, thimerosal had been removed from most vaccines in the U.S. and other high-income countries; it can still be found in some seasonal influenza vaccines and other adult vaccines. In areas of the world with fewer resources, however, thimerosal is still widely used as a vaccine preservative.

At the time of the joint statement by the AAP and USPHS, there were no studies that had evaluated the potential harm of ethyl mercury -- as opposed to methyl mercury -- obtained through vaccines.

Since then, however, studies looking for harms from thimerosal-containing vaccines have failed to find such associations, whereas research has consistently demonstrated serious neurotoxic effects from methyl mercury.

The consistent lack of evidence of any harm from thimerosal in vaccines formed the basis of the AAP's reversal of its 1999 stance, and Cooper and Katz suggested that the academy would not have issued the original statement with than knowledge in-hand.

Potential Fallout from a Thimerosal Ban

In another commentary, Walter Orenstein, MD, of Emory University in Atlanta, and colleagues explained the benefits of keeping thimerosal as an option for vaccines.

"Thimerosal allows the use of multiuse vials, which reduce vaccine cost and the demand on already constrained cold-chain systems," they wrote.

They said banning use of the preservative could harm the world's vaccine supply by increasing manufacturing costs, reducing manufacturing capacity because of the need to switch to single-dose vials, increase waste from single-dose packaging, and strain transportation and storage space.

"The resulting cold-chain requirements would be untenable in many areas of the world because of programmatic challenges and increased workload," Orenstein and colleagues wrote.

"The continued benefits of thimerosal use in vaccine manufacturing clearly outweigh any perceived risks," they added.

In its recommendations, the WHO's SAGE noted that there are no viable alternatives to thimerosal.

"Replacement of thimerosal with an alternative preservative may affect the quality, safety, and efficacy of vaccines; re-registration would be required by the National Regulatory Authority in each jurisdiction where a reformulated product was intended to be used; currently available alternative preservatives interacted in unpredictable ways with existing vaccines, and there are no consensus alternative preservatives for the near- or mid-term," according to the guidance.

Ultimately, it stated, a thimerosal ban could threaten access to certain vaccines -- such as tetanus toxoid, diphtheria-tetanus-whole cell pertussis, and hepatitis B vaccines -- around the world, particularly in developing countries.

"There would be a high risk of serious disruption to routine immunization programs and mass immunization campaigns if thimerosal-preserved multidose vials were not available for inactivated vaccines, with a predictable and sizable increase in mortality, for exceedingly limited environmental benefit," the statement read.

In a third commentary, Katherine King, PhD, of St. Michael's Hospital in Toronto, and colleagues noted that "some nongovernmental organizations oppose [removing the ban on thimerosal from vaccines from the draft treaty], arguing that it would be unjust to allow thimerosal to be used in low- and middle-income countries when its use has been all but phased out of wealthier nations."

"This critique is misplaced," they wrote, adding that there is no threat of injustice because of the lack of evidence of health risks.

"Rather," they wrote, "the real threat of injustice comes from considering the removal of this currently necessary and irreplaceable compound from the global vaccine supply, and the avoidable increases in morbidity and mortality that would inevitably result from disruptions to vaccination programs targeting already marginalized populations in low- and middle-income countries."

All authors of the AAP's statement of endorsement have filed conflict of interest statements. Any conflicts have been resolved through a process approved by the academy's board of directors. The AAP said it has neither solicited nor accepted any commercial involvement in the development of the content of the statement.

Cooper and Katz reported that they had no conflicts of interest.

King and colleagues reported that they had no conflicts of interest.

Orenstein and colleagues reported that they had no conflicts of interest.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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